1. Field of the Invention
This invention relates to a remaining ink volume detector such as is used in ink jet recorders and the like, and particularly to an ink jet recorder that comprises a remaining ink volume detector that can definitely detect whether or not there is a remaining volume of ink in an ink cartridge.
2. Description of the Related Art
Ink jet recorders are known wherein ink supplied by an ink cartridge is ejected from a print head. In this type of ink jet recorder, a remaining ink volume detector is provided for detecting remaining ink volume in the ink cartridge. This remaining ink volume detector is usually configured with an optical sensor comprising a light emitting unit that focuses a light beam on the transparent or semitransparent case of the ink cartridge, and a photodetector that receives reflected light from the ink cartridge. The remaining ink volume detection by the optical sensor is performed, when the print head, on which is mounted the ink cartridge, has been moved by the carriage to a detection position opposite the optical sensor, at that detection position. The light beam from the light emitting unit of the optical sensor is directed against the side wall surface of the ink cartridge, and the presence or absence of a remaining ink volume is determined using the fact that the reflected light reflectance from the ink cartridge side wall surface changes depending on the presence or absence of ink.
Unfortunately, immediately after the carriage has moved to the detection position, waves are generated on the fluid surface of the ink in the ink cartridge due to vibration induced by carriage movement. Because the remaining ink volume is detected by the optical sensor under these conditions, the optical sensor recognizes ink adhering to the inner walls of the ink cartridge at positions either above or below the actual ink fluid surface, giving rise to the fear of producing erroneous detection results.
In Japanese Patent Application Laid-open No. 8-112910 is disclosed an optical remaining ink volume detector that detects remaining ink volumes by measuring, at multiple times, changes in optical reflectance at the interface between an ink cartridge and an ink absorber inside the ink cartridge. However, there is wide variation in the position where the ink remains in the ink absorber, and it is very difficult to accurately detect changes in optical reflectance from the interface between an ink cartridge wall and an ink absorber.
An object of the present invention, which was devised in order to resolve the problems with the prior art noted above, is to provide an ink jet recorder of the type wherein an ink jet head and an ink cartridge are made to sweep across a recording medium by means of a carriage, wherein the remaining ink volume can be detected with high precision.
According to an aspect of the present invention, an ink jet recorder is provided which comprises: an ink jet head for ejecting ink onto a recording medium; an ink cartridge for supplying ink to the ink jet head, provided on the ink jet head so as to be detachable; a carriage that holds the ink jet head, capable of sweeping across the recording medium; a detector for detecting whether or not ink fluid level in the ink cartridge is at a prescribed level; a display for indicating ink cartridge replacement; and a controller for controlling the detector and the display so that the detector performs at least two detection operations and, when two of those at least two detection operations indicate an ink fluid level lower than the prescribed level, the display displays ink cartridge replacement thereon.
The recorder according to the present invention performs at least two remaining ink volume detection operations and determines that insufficient ink remains in the ink cartridge when the results of at least two of those detection operations indicate an ink fluid level lower than a prescribed level. Therefore, erroneous ink level determinations can be minimized even though ink waves develop inside the ink cartridge due to the movement of the carriage in the sweep direction.
In the recorder according to the present invention, the ink cartridge mentioned above may be formed of a light-transmitting material. The detector mentioned above may be an optical sensor that directs light onto the inner side surface of the ink cartridge and detects the light reflected back therefrom. Depending on whether there is or is not ink on the surface of the inner wall of the ink chamber inside the ink cartridge, that is, on whether an ink layer or an air layer is present there, the refractive index or, alternatively, the reflectance changes at the interface between the inner wall surface and the ink layer or air layer. The optical sensor detects variations in the amount of light received as reflected light from the surface of the inner wall of the ink chamber. The detector may be a sensor that measures electrical resistance between electrodes.
The controller is capable of performing two detection operations with the detector and, if both of these detection operations indicate an ink fluid level short of the prescribed level, indicating ink cartridge replacement on the display. Thus processing can be done simply and in a short time. If only one of the two detection operations indicates an ink fluid level short of the prescribed level, then a third detection operation may be performed by the detector, and ink cartridge replacement indicated on the display if two out of the three detection operations indicate an ink level short of the prescribed level.
Alternatively, the controller may perform three detection operations and indicate ink cartridge replacement on the display if two out of those three detection operations indicate an ink fluid level short of the prescribed level.
The ink jet recorder according to the present invention may comprise a purge unit that has a suction cap which covers the ink jet head and sucks ink from the head. When that is the case, if the optical sensor is attached to the purge unit, the controller may perform detection operations by the detector described above while the purge unit is performing a purge operation. In other words, in that case, the ink jet recorder is able to perform purge operations and remaining ink volume detection operations simultaneously any time the ink jet head is not recording on the recording medium.
The ink jet recorder according to the present invention may also comprise a timer, whereupon each of the at least two detection operations by the detector can be performed after a prescribed time has elapsed since the last detection operation, as measured by the timer. The prescribed time may be made a time interval that does not coincide with the wave-generation period for the ink inside the ink cartridge. For example, if it takes 0.2 seconds for the carriage holding the ink carriage to move (sweep) across an A4 size paper sheet in its widthwise direction, the wave generation period is about 5 Hz. Considering a reflection of the wave from a inner wall of the cartridge, the wave generation period might be slightly higher than 5 Hz. Thus, by adjusting the time interval between the two detection operations, in cases where the first detection operation indicates an erroneous result due to the influence of ink waves inside the ink cartridge, results differing from the first results can be indicated by the next detection operation, so that true detection results can be produced that take into consideration those later detection results. By adjusting the prescribed time interval in this manner, furthermore, it is not necessary to provide a waiting time to allow the waves inside the ink cartridge to subside, wherefore remaining ink volume detection can be done quickly.
The ink cartridge described in the foregoing may be made so as to have a first ink chamber for supplying ink to the ink jet head and a second ink chamber allowing liquid to communicate therebetween, the first ink chamber being smaller in capacity than the second ink chamber. In that case, the detector described earlier can detect whether or not the ink fluid level in the first ink chamber is at a prescribed level. Thus the formation of ink waves can be suppressed by making the volume of the first ink chamber small.